The invention relates broadly to a camera lens for a photographic or a film camera and, more particularly relates to a lens for a camera for capturing three-dimensional images.
The ability to capture and reproduce a three-dimensional image, either for three-dimensional photography or for three-dimensional films, is known from the prior art. One known way of capturing a three-dimensional image involves the use of a stereo camera, which is a camera with two or more lenses and an individual image sensor for each lens. The use of multiple lenses corresponds to human stereo vision enabled by both eyes.
Such a three-dimensional image is useful for a number of applications, in particular those involving agricultural machinery and vehicles. WO 2007/031093 describes the use of a three-dimensional image for controlling the pick-up device of a baler. The captured three-dimensional image is analyzed to determine a height profile of a crop string, thereby enabling an automated pick-up by the baler.
EP 2 368 419 A1 describes using a stereo camera on a self-propelled agricultural machine for detecting structures identified by their geometry in a crop field. This enables automatically steering that agricultural machine according to the position of the detected structures. It is evident that the capture and processing of three-dimensional images permits an increasing automation in the operation of a wide variety of agricultural machines, which are employed not in a controlled factory environment but rather in the dynamic environment of an outdoor field.
As those skilled in the art will realize, however, that agricultural machines are used outdoors in terrain that may be rugged and likely exposed at times to harshly different weather conditions. Harshly different weather conditions, beside the aspect that the material handled by the machines is often heavy and cumbersome, significantly increases the likelihood of mechanical shocks and vibrations experienced by the agricultural machine and all its components and instruments. These naturally include the stereo camera for capturing the three-dimensional image and any camera lenses it has as components. In addition to these mechanical stresses, the temperature range in which the agricultural vehicle and its components and instruments must operate under also is much wider than that temperature range found in a factory hall situation.
Stereo cameras, and especially their lenses, are especially susceptible to mechanical impacts and vibrations.
A contemporary lens consists of multiple lens elements arranged in a predefined relative mechanical arrangement, in particular with a predefined distance between the lens elements. Any deviation from this arrangement leads to a loss of calibration and reduced image quality. Loss of calibration and reduced image quality is even more problematic for stereo cameras than for regular cameras with only one lens. In particular, arrangements in which the lenses of the camera are aligned in parallel, the so-called parallel configuration, as opposed to the converged or toed-in configuration, requires a calibration with little tolerance for error.
Thus, in a case of a relative displacement, a recalibration likely is necessary, which typically entails returning the camera for servicing. Beside the direct cost of servicing, this also results in at least the camera being out of operation for a certain time. Of course, the risk of subsequent losses of calibration in the future is not mitigated by such a recalibration.
Camera lenses are known from the prior art in which the retainer, i.e., the lens cap or the cover of the casing itself, is screwed on the barrel of the retainer and presses on the lens elements of the camera lens. In such situations, however, measurements have determined that even though such a screwed-on retainer will exert a sufficient clamping force on the lens elements at room temperature, the thermal expansion of the retainer at extremely high and extremely low temperatures may lead to vanishing of the clamping force on the one hand and rising even above a breaking force on the other hand. Therefore, the known lenses are applicable only in a narrow temperature range.
U.S. Pat. No. 4,203,661 discloses a camera lens in which a spring is arranged within the housing of the camera lens. This spring, however, only acts as a resistance to a focusing ring of the camera lens and does not act on the lens elements of the camera lens in any way.